
\begin{tikzpicture}[scale=2.4]
  \coordinate[label=above:$A$] (A) at (75:1);
  \coordinate[label=below:$B$] (B) at (-120:1);
  \coordinate[label=below:$C$] (C) at (-50:1);
  \coordinate[label=above:$O$] (O) at (0,0);
  \coordinate[label=left:$P_1$] (P1) at ($ (C)!1! 90:(O) $);
  \coordinate[label=right:$P_2$] (P2) at ($ (P1)!2!(C) $);
  \pic[mark angle={blue}{3mm}{1}] {angle=B--A--C};
  \pic[mark angle={blue}{3mm}{1}] {angle=B--C--P1};
  \pic[mark angle={red}{3mm}{1}] {angle=B--O--C};
  \pic[mark angle={green}{3mm}{1}] {right angle=P2--C--O};
  \draw (O) circle (1)
      (B) -- (A) (A) -- (C) (C) -- (B) (P1) -- (P2);
  \draw[dashed] (O) -- (B) (O) -- (C);
\end{tikzpicture}
